Many mechanical systems incorporate belt and roller systems for a variety of purposes. For example, some machines use a belt as an operative structure to work on material or a workpiece. In other applications, belts simply move materials or goods from one location to another. Also, belts are often employed simply to couple a power source to a machine to transmit working power thereto. In all of these applications, a belt is in the form of a continuous loop which is supported at opposite reversing ends by rollers so that the belt may cycle therearound. In some applications, of course, intermediate rollers are positioned between the two end rollers to help support the belt during use.
Regardless of the application, proper operation of these systems requires that the belt remain centered on the various rollers over which it is trained. It is well-known that belt drift may occur as the belt tracks around the rollers so that the belt may move laterally. Such belt drift, not only may interfere with proper operation of the system, but also poses a risk of injury to workers around the equipment. This is because improper alignment of the belt on the rollers may damage the belt causing it to break during use. Accordingly, various structures have been designed to reduce or eliminate belt drift during operation.
One common example of such a technique is the use of crowned rollers to support the belt. It is known that the use of shaped rollers, either crowned or convex, can sometimes reduce the tendency of the belt to drift. Other techniques attempt to physically constrain the belt during movement. For example, a roller may be provided with opposed lips between which the belt is positioned. However, should the belt track up onto the lip, damage to the belt and attendant danger to workers results. The belt may also be constrained between brackets, but due to the flexibility of the belt, this technique is not favored. Other attempts to resolve the problem of belt tracking include the incorporation of buttons, pins or rivets onto the belt itself with these structures being received in guides on the rollers. also, electronic tracking and adjustment are described, for example, in my U.S. Pat. No. 5,101,980 issued Apr. 7, 1992 and entitled Magnetic Separator Assembly For Use In Material Separator Equipment.
One of the most difficult belt tracking applications is encountered where the length of the rollers is large relative to the distance of separation between them (the "roller distance"). Magnetic separators are a prime example of equipment that requires a short roller distance. In a magnetic separator, a cylindrical magnetic roller is located at a downstream region of a conveyor and a cylindrical idler roller is located at an upstream end. A relatively thin conveyor belt encircles the magnetic roller and the idler roller. These belts are short, wide belts constructed of very thin materials. Particulate material having magnetic and non-magnetic components to be separated by the magnetic roller is deposited on an upper conveying portion of the belt so that it moves in a downstream direction across the magnetic roller. Magnetic components in the material are attracted to the magnetic roller and thus have different discharge trajectories than non-magnetic components. The use of thin belt material is necessary to achieve strong magnetic forces at the magnetic roller. Thus, the roller distance must be minimal to avoid sagging of the belt due to the load placed by the material as it is advanced. The use of shaped rollers is not generally effective where there is such a short roller distance.
A new technique for providing self centering adjustment of conveyor belts, especially in magnetic separators, has been developed. This technique is based upon the principle that a belt will move toward a higher stress point, which is the principle employed by crowned rollers to cause better belt tracking. In the new technique, however, the increased stressed region is caused by moveable sections of the idler roller which are pivotally secured to the center of the roll so that each section may pivot about a pivot axis that is orthogonal to the axis of rotation of the idler roller. When a belt drifts to one end of the idler roller, these sections are moved radially inwardly. This causes the opposite ends of the sections to move radially outwardly thereby increasing the stress on the belt and causing it to move back toward the center of the roller. It is to this technique that the present invention is directed.